A load signal, which is corrected with respect to exhaust-gas recirculation and which is proportional to the fresh air mass inducted per revolution, is needed especially for computing the fuel quantity to be injected. This is so because errors in the corrected load signal lead, inter alia, to errors in the mixture composition and therefore to increased toxic substance emissions.
Methods are known for considering the influence of an exhaust-gas recirculation in a load detection for engine controls of spark-injection engines wherein the load detection is based on intake pipe pressure. In these methods, a corrective factor from a rpm-dependent and load-dependent characteristic field is used to correct the injection time for external exhaust-gas recirculation. However, these methods only provide good results for steady-state conditions and have several disadvantages.
The corrective factor is always dependent upon the operating point of the internal combustion engine, that is, the corrective factor is dependent upon the rpm and the load of the engine with the load being detected, for example, from the angle of the throttle flap. This requires, for example, during an application, a new adaptation of the corrective characteristic field in a complex manner for each change of the exhaust-gas recirculation rate.
Furthermore, the correction of the injection time is only correct during steady-state operation. Dynamic residual errors in the mixture composition are unavoidable especially for changes in the operating point, that is, for changes of the rpm and the load caused by changes of the throttle flap angle. This causes a disadvantageous deterioration of the exhaust-gas values of the engine. Furthermore, such known methods operate only imprecisely when changes of the ambient pressure occur, such as when operating the engine at different elevations. Finally, it is disadvantageous that these methods do not make possible output signals which form the basis for other functions such as the ignition angle correction or a torque interface.
Furthermore, a method for detecting the load signal of an internal combustion engine is known from German published patent application 195 25 815. In this method, the load signal of the engine is corrected in dependence upon intake pipe pressure, exhaust-gas pressure, rpm and from the position of the EGR valve. However, it is disadvantageous in this method that it likewise only correctly operates for steady-state conditions and, furthermore also exhibits residual errors when changes of ambient pressure occur.